Self-adhesive tapes are used to a great extent in libraries and archives where often books, documents, charts, drawings, engravings and other paper records are stored which are damaged and which need to be repaired or preserved. For example, torn pages which are unavoidable in frequently used books can be repaired with adhesive tapes in almost invisible fashion. Likewise, thanks to these tapes, pages can be inserted in perfectly flat condition, torn-out pages reattached in a book, single pages joined into layers for sewing, damaged edges of documents repaired or book spines stripreinforced inside. However, these adhesive tapes are also frequently used in other areas, e.g. by art dealers and picture framers to secure prints, drawings, paintings, and aquarelles or photos to the passe-partout and for back-lining and sealing the backs of pictures after their insertion, so that the framed picture will be protected against the infiltration of dust particles and insects.
To achieve all these purposes it is important for the base of the adhesive tapes to consist of paper, as foils are unsuitable as bases in this respect. Nonageing grades of paper which through uniform felting of relatively long fibers display a high tensile strength and toughness are preferred. It has been found advantageous in practice to provide for base paper of the tape in at least two different thicknesses, namely a very thin transparent paper weighing 10-30 g/m.sup.2 by means of which almost invisible adhesions can be obtained, and a somewhat heavier, opaque paper weighing about 30-50 g/m.sup.2, which can be used for those adhesions which must withstand higher loads.
Besides the base paper, the self-adhesive material of the tape also must meet special requirements. It should display good instant adhesive power on paper, good cohesion (internal strength) and as much as possible high ageing stability. Furthermore, it has lately also become desirable that the self-adhesive material on the one hand remains insensitive to the usual atomospheric moisture and temperature fluctuations in nonair conditioned rooms, while showing constant adhesive properties, and on the other hand can be dispersed in water even after long-term adhesion, without damaging the joined substrates by tearing out their fibers. The self-adhesive materials of the hitherto known paper-adhesive tapes, to be sure, possess the required adhesive properties and have on the whole sufficient ageing stability, but they cannot be dispersed in water so that, once a tape is affixed, it can no longer be detached from the substrate.
Dispersible or water-soluble self-adhesive materials are well known in themselves; they are generally used for water-detachable self-adhesive labels and double-faced adhesive paper tapes. By way of example, DE-PS Nos. 2,214,293 and 2,236,575 describe dispersible self-adhesive materials for labels, containing acrylate copolymerisates, alkali salts of polyacrylic acids and polyvinyl methyl ethers. Dispersible and water-soluble self-adhesive materials for double-faced adhesive tapes to make endless paper webs are described in several patent specifications. These self-adhesive materials consist of: a mixture of polyvinyl pyrrolidone with crosslinking agents and polyols or polyalkylglycol ethers as softeners (U.S. Pat. No. 3,096,202); of epoxidized rubber-like polymers with water-soluble secondary monoamines (U.S. Pat. No. 3,661,874); of a conversion product (partial ester) of a methyl vinyl ether-maleic acid anhydride copolymerisate an alkylphenol polyglycol ether and nonconverted alkylphenol polyglycol as softeners (DE-PS No. 2,311,746); of a mixture of arylic acid-alkoxyalkyl acrylate copolymerisates and polyethylene glycol derivates, as well as polyethylene glycols and polypropylene glycols as softeners (U.S. Pat. No. 3,441,430); of arylic acid acrylate coplymerisates neutralized with alkanolamines, sortening polyoxyethylene compounds and acid colophonium resins neutralized with alkanolamines (DE-OS No. 2,360,441); of acrylic acid acrylate copolymerisates partially neutralized with soda lye (NaOH) and tertiary ethoxylated N-alkyl alkane diamine (DE-PS No. 2,904,233); or of acrylate vinyl carboxylic acid copolymerisates with ethoxylated (alkyl) phenols and ethoxylated alkylmono- and alkyldiamines, in which the acid in the copolymerisate is preponderantly neutralized with potassium hydroxide (EP-PS No. 58,382).
Among these well-known self-adhesive materials in variable compositions there is no version which meets the requirements of a high-grade paper-adhesive tape. To be sure, all these self-adhesive materials are dispersible or water-soluble, but they have no adequate ageing stability. Moreover, the water-soluble types are mostly so highly water-soluble that in high atmospheric humidity the adhesion spot will become loose, whereas the dispersible types become so thoroughly attached to the paper substrates that in the event of their redispersion they will cause partial damage to the substrates by tearing out the fibers.
Accordingly, there is a need in the art for a self-adhesive composition, and paper tape coated therewith, which has the required adhesive properties, has excellent ageing stability, and water dispersibility permitting removal without destroying the archival quality of the subject repaired by the tape.